The present invention relates to a particulates removing unit used for a pretreatment of an exhaust gas produced from a semiconductor production process, prior to subjecting the gas to a harm removing process. More particularly, the present invention relates to a removing unit particularly suitable for Chemical Vapor Deposition (hereinafter to be abbreviated as CVD) type steps involved in semiconductor production processes, to a filter unit capable of reducing a load on the removing unit itself and a load on a subsequent harm removing equipment, even when the amount of particulates, including impurities such as reaction product, other mist and dust in a discharged exhaust gas, is large, by enabling a long-term removal of the particulates, and to a filter incorporating the filter unit.
The semiconductor production process includes an ion implantation method, a metal etching method using aluminum and the like, a CVD method and the like. In any of these methods, an exhaust gas is generated, which contains a toxic gas such as hydrofluoric acid, silane gas, tetraethoxysilane (hereinafter to be abbreviated as TEOS), ammonia and the like, particulates including impurities such as reaction product and the like, and other mist and dust. To remove the particulates, a harm removing equipment is generally installed.
Conventional harm removing equipments remove particulates by adsorption thereof onto an adsorbent (e.g., ion exchange resin and zeolite), adsorption thereof onto water by the use of a water scrubber, through decomposition by combustion by a burner, and the like. When particulates are contained in an exhaust gas, however, the harm removing equipment using an adsorbent defectively shows a greater pressure loss per unit area, and the harm removing equipment using a water scrubber defectively necessitates disposal of sludge of adsorbate, and the harm removing equipment by combustion defectively shows a clogged nozzle of a burner and staining of a combustion chamber. These defects in turn give rise to the need of periodical cleaning of the harm removing equipment and exchange of an equipment, on which a great load has been applied. In particular, the CVD method is associated with a large amount of particulates in an exhaust gas from the semiconductor production process, which increases cleaning frequency and noticeably shortens the service life of the equipment.
The present inventors have proposed a vacuum exhaust gas filter system in JP-A-7-256022 as a pretreatment device for the above-mentioned harm removing equipment. They have later found that a filter used in a semiconductor production process by the CVD method becomes clogged in about 3 days to 3 weeks. Accordingly, the development of a filter unit is desired, which is applicable even when the amount of particulates in an exhaust gas is large.
It is therefore an object of the present invention to provide a filter unit capable of removing a great amount of particulates in an exhaust gas produced in a semiconductor production process and the like, over a long period of time, thereby facilitating maintenance of the harm removing equipment and reducing the cost born by the user, and to provide a filter using this filter unit.
Such object can be conveniently achieved by the present invention described in the following.
(1) A filter unit for removing particulates in a gas to be treated, which comprises a gas impermeable bulkhead that forms a channel through which the gas advances in the filter unit at least one round, and a filter member laminated on at least one side surface of the bulkhead, without closing the channel.
(2) A filter unit preferably having a filter member containing a nonwoven fabric having a density of 0.005-0.4 g/cm3, which fabric is prepared using a fiber having 0.1-8 mmol/g of an ionic group.
(3) The filter unit preferably having a means for retaining or circulating a coolant.
(4) A filter comprising the filter unit of (1) above and a second filter unit, wherein the second filter unit has a cylindrical filter member having a central duct, the filter unit of (1) above and the second filter unit being connected to each other, such that the gas that has passed through the filter unit of (1) above proceeds to the central duct from the periphery of the cylindrical filter member.
(5) The filter wherein the above-mentioned filter member in the filter unit of (1) above and/or the above-mentioned cylindrical filter member (4) comprise(s) a nonwoven fabric having a density of 0.005-0.4 g/cm3, which fabric is prepared using a fiber having 0.1-8 mmol/g of an ionic group.
(6) The filter wherein the filter unit of (1) above and/or the second filter unit of (4) above have/has a means for retaining or circulating a coolant.